Effect of Epitaxial Growth of Gold Nanoparticles on Si Substrates on Adhesion of Electrolessly Deposited Metal Films
At the first step of the two-step process, Au nanoparticles were deposited on a p-Si(100) substrate by electroless displacement deposition using a HAuCl4 solution containing HF. At the second step, the nickel-phosphorus alloy (Ni-P) film was electrolessly formed on the Si substrates by using NiSO4 as a metal salt and NaPH2O2as a reducing agent. The adhesion of the electrolessly deposited Ni-P films on Si substrates was examined by a tape test based on Japanese Industrial Standard JIS H8504 corresponding to ISO 2819. The adhesion was evaluated by maximum Ni-P film thickness that occurred no peeling by the tape test. We analyzed the interfacial structure of Au/Si by X-ray diffraction (XRD, Rigaku Ultima IV) and transmission electron microscopy (TEM, JEOL JEM-2100).
Figure 1 shows the XRD patterns of Au nanoparticles on p-Si(100) substrates. Only Au(200) diffraction line was obtained for the sample immersed in the Au-deposition-solution for 120 s (Fig.1 (a)). The cross-sectional TEM observation of Si wafer Au-nanoparticle-deposited for 210 s revealed that Au nanoparticles epitaxially grew on Si and each particle was single crystalline. At the interface between Au and Si, Au-Si alloy formation was observed by TEM and XPS (3). Farther deposition yielded Au(200) and (111) diffraction lines such as Fig.1 (b) for immersion deposition time of 240 s.
Figure 2 shows the maximum film thickness (adhesion) of electrolessly deposited Ni-P alloy films on Si substrates as a function of Au nanoparticle deposition time. The maximum film thickness increased with deposition time of Au nanoparticles, reached maximum at 120 ~ 210 s, and decreased afterwards. This result indicates that the electrolessly deposited Ni-P films have high adhesion in case that the Au nanoparticles epitaxially deposited on Si substrates. The growth of polycrystalline Au on epitaxially deposited Au nanoparticles on Si decreases the adhesion of the electrolessly deposited Ni-P films.
In conclusion, it was revealed that single crystalline Au nanoparticles epitaxially grown on Si substrates yield high adhesion of electrolessly deposited metal films.
The present work was partly supported by KAKENHI (26289276) from JSPS.
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